The invention relates to systems for controlling noise and vibration and more particularly to an active control system for reducing engine noise and vibration which includes a rotating electromechanical energy converter output device. Control of a vibrating body has previously been accomplished in the prior art by detection of the vibration and application of a force against the detected vibration as seen in, e.g., Japanese Patent No. 58-144231. In order to provide active noise and vibration control, a multitude of vibration generators is required. As a consequence, the weight of these devices becomes appreciable and undesirable, even more particularly so in aircraft applications.
In a conventional shaker, a force is applied to the structure by reaction against an accelerating mass. The force is the product of the mass and the acceleration. In order to limit the displacement of the mass (which is proportional to the acceleration) the mass cannot be reduced below some limits set by the practicality of the suspension of the mass.
Accordingly, it is an object of the present invention to remove the aforementioned constraint on mass reduction in vibration generator design.
In accordance with a first embodiment of the invention, an electric motor is provided with its stator rigidly attached to the structure to be vibrated. An input current is applied through the windings which input current is modulated in proportion to the desired torque in order to vibrate the structure by application of an oscillatory torque.
A further embodiment of the present invention utilizes a fast spinning rotor which is braked electrically with a modulated current to produce the oscillatory torque.
These and other objects and advantages of the present invention are specifically set forth in or would become apparent from the following detailed description of preferred embodiments of the invention when read in conjunction with the accompanying drawings in which: